First-in, first-out memory

ABSTRACT

A FIRST-IN, FIRST-OUT STORAGE DEVICE IN WHICH THE FIRST-IN, FIRST-OUT FUNCTION IS PERFORMED BY WRITING INFORMATION IN THE FORM OF A MAGNETIC DOMAIN INTO AN UNKNOWN LOCATION IN A DATA REGISTR OF THE MAGNETIC FILM TYPE UNDER THE INFLUENCE OF A MARKER MAGNETIC DOMAIN DISPOSED IN A CONTIGUOUS REGISTER.

Jam. 5, 1971 i D. R. HADDEN, JR 3,553,661 1 FIRST- IN FIRST-OUT MEMORYFiled June 27, 1967 8 Sheets-Sheet 1 v FIG.)

INVENTOR, FIG DAVID R. HADDEN JR.-

ATTORNEYS.

1 D. R. HADDEN, JR fi fi FIRST-IN, FIRST-OUT MEMORY Filed June 27, 196?8 Sheets-Shem :3

INVENTOR, DAV/D R ADDEN JR.

ATTORNEYS Jan. 1971 D. R. HADDEN, JR 3,553,561

FIRST-IN FIRST-OUT MEMORY Filed June 27, 1967 8 Sheets-Sheet rs FIG. 5 I2 3 4 WRITE HT 0 I INVENTOR, 0 Wu H. HADDEN JR.

A T TORNE YS.

Jan. 5, 1971 D. R. HADDEN, JR 3,553,661

FIRST-IN, FIRST-OUT MEMORY I Filed June 27,- 1967 8 Sheets-Sheet 4INVENTOR,

DAVID R. HADDEN JR.

ATTORNE YS,

Jan. 5, 1971 D. R. HADDEN, JR 3,553,551

FIRST-IN. FIRST-OUT MEMORY Filed June 27, 1967 V 8 Sheets-Sheet 5 'V 40aF/G. 82- 26 47 A 43 I A A v I a h INVENTO DAV D R. HADDEN AT TORNE Y5Jan. 5, 1971 D. R. HADDEN, JR I 3,5

I FI'RsTJN, FIRST-OUT MEMORY Filed June 27, 1967 8 Shets-Sheet 7 v 53Cm-- 0 90 X A 4 37 36 YINVENTORG FIG DAVID R. H'ADDEN JR.

BY jaw/ah 1 ATTORNEYS.

Jan. 5, 1971 p. R. HADDEN, JR 3,553,661

FIRST IN, FIRST-OUT MEMORY, Filed June 27, 1967 8 Sheets-Sheet 8mvENToR, DAVID R. HADDEN JR.

BY p4 WWW J United States Patent Office 3,553,661 Patented Jan. 5, 1971U.S. Cl. 340174 13 Claims ABSTRACT OF THE DISCLOSURE -A first-in,first-out storage device in which the first-in, first-out function isperformed by writing information in the form of a magnetic domain intoan unknown location in a data register of the magnetic film type underthe influence of a marker magnetic domain disposed in a contiguousregister.

BACKGROUND OF THE INVENTION In the asynchronous transfer of data in thedigital communication field, data buffer memories of the firstin,first-out type are useful. Such memories accomplish the task of handlingdata in the order in which it is received.

Prior first-in, first-out emories generally have been random accessdevices in which one must keep track of the location in which theinformation is to be written and also the location in the memory fromwhich that information is to be read. In order for the random access tofunction as a first-in, first-out memory so as to permit the randomaccess memory to handle data sequentially (firstin, first-outoperation), considerable extra circuitry must be added.

The memory of the invention, on the other hand, includes a pair ofcontiguous shift registers, which inherently are characterized bysequential access, positioned backto-back. One of these registerscontains a magnetic marker domain which is movable along the register inresponse to properly applied magnetic fields. Binary data can be writteninto a data register disposed in proximity with the marker registerunder the influence of the marker domain. A given data bit is writteninto the data register at some location therein determined by theposition occupied by the marker domain along the marker register. Thedata bit thus written into the data register depends upon the presenceor absence of a domain-controlling current which determines whether ornot the marker domain is transferred by magnetic domain growth into thedata register.

The device of the invention is much less complicated and expensive thanthe modified random access memories of the prior art.

SUMMARY OF THE INVENTION The first-in, first-out storage device of theinvention consists of a marker register and a data register. Eachregister includes a thin multisegment, zig-zag strip or channel ofmagnetic material disposed on a background material such as tape, whicheither is non-magnetic or higher coercive force than the channel. Thetwo strips or channels are contiguous and are disposed so that regionsof intersection of adjoining segments of a given channel are in closeproximity with corresponding regions of intersection of adjoiningsegments of the other channel. Since the magnetic thin film within thechannel is of low coercive force, for the magnitude of fields appliedduring operation of the shift register, only that portion of the filmwithin the channel is capable of being switched.

These fields are of such magnitude as to cause the growth of existingdomains without creating new ones.

Each of the channels is traversed by a pair of domaincontrollingelectrical conductors, one passing over the uppermost regions ofintersection of adjacent segments and the other passing over the lowerregions of intersection of adjoining segments. In one embodiment of theinvention, a .fifth control conductor is added and is disposed betweenthe two registers. A pair of mutually perpendicular magnetic biasingfield producing means also is disposed adjacent the two channels.

A marker bit of information is represented by a small magnetic domainthe direction of magnetization of which is opposite that of the channel;this marker initially is located at one of the regions of intersectionof adjoining segments of the low coercive force channel of the markerregister. Depending upon the direction of the magnetic biasing fieldalong the easy axis of magnetization of the domain, the marker domaincan be grown or shrunk.

Owing to the proximity of the two channels, if the marker domain isgrown in the direction of the second (data) channel, the marker domaincan be transferred into the data register, provided, of course, that abiasing magnetic field of the proper direction to achieve domain growthis supplied to the two registers. In this manner, a ONE can be writteninto the data register at a location determined by the position of themarker in the marker register. By applying a current to an appropriatedomain controlling conductor of the data register which provides amagnetic field bucking the magnetic field of the marker domain, theaforesaid inter-register domain transfer can be inhibited and a ZEROwritten into the data register at a position dependent upon the positionof the marker domain.

By applying currents to the wires of the two registers in propersequence, the data written into the data register in the form ofmangnetic information can be shifted past an output coil or othersensing means in the order in which the data was written therein.Furthermore, the marker domain in the marker register is shifted alongwith the data so that the position of the marker domain will correspondto the first empty data position (the position nearest the output) inthe data register.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view showing anembodiment of the invention;

FIGS. 2a-2i are diagrams illustrating the basic shift operation and thebasic write operation for the device shown in FIG 1; i

FIGS. 3a3e are diagrams showing the basic shift operation for a magneticdomain of opposite direction to that shown in FIG. 2;

FIGS. 4a-4e are diagrams showing the basic shift operation where thedomain is shifted to the right, rather than to the left, as in the caseof FIG. 2;

FIG. 5 are waveforms of the currents used in driving the magnetic coilsand the various control wires during the write operation shown in FIG.2;

FIGS. 6a6i are diagrams showing the basic read op eration of the deviceshown in FIG. 1;

FIG. 7 are waveforms of the currents used in driving the magnetic coilsand the various control wires during the read operation shown in FIG. 6;

FIGS. 8a-8i are diagrams showing a typical write operation for amodification of the embodiment of the invention shown in FIG. 1;

FIG. 9 are waveforms of the driver currents for the modified device ofFIG. 8 during the write operation;

FIGS. 10a-1 e are diagrams showing a read operation for the modifieddevice shown in FIG. 8;

FIG. 11 are waveforms of the driver currents for the modified device ofFIG. during the read operation;

FIGS. 12a-12f are diagrams of a modified form of the device shown inFIG. 8 illustrating the write operation; and

FIGS. l3a-l3f are diagrams of the modified form of the device shown inFIG. 12 illustrating the write operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawing, a first-in, first-out storage device is shown which consists oftwo separate registers and 30, referred to hereinafter as a markerregister and a data register, respectively. Each register includes athin rnulti-segment, zig-zag strip or channel 21 and 31 of magneticmaterial disposed on a background material 24 such as tape, which eitheris non-magnetic or of higher coercive force than the channel. Thechannels 21 and 31 of the respective registers 20 and are contiguous andare disposed so that alternate regions of intersection of adjoiningsegments of a given channel are in close proximity with correspondingregions of intersection of adjoining segments of the other channel.

In the embodiment of the invention shown in FIGS. 1, 2 and 6, each ofthe channels is traversed by a pair of domain-controlling electricalconductors, one passing over the upper regions of intersection ofadjacent segments and the other passing over the lower regions ofintersection of adjoining segments. For example, in the device shown inFIGS. 1 and 2, in which the two channels are sawtooth-shaped anddisposed back-to-back, the domain-controlling wire 25 passes over theupper apices of marker channel 21 and the other control wire 26 passesover the lower apices of this channel. Similarly, control wire passesover the upper apices of data channel 31 and control wire 36 passes overthe lower apices of data channel 31.

A pair of mutually perpendicular magnetic fields can be selectivelyproduced in the vicinity of the channels by means of appropriate coils,not shown, arranged to produce mutually perpendicular magnetic fields Hand H The means for producing magnetic fields H and H, may, for example,comprise a first set of Helmholtz coils connected to a first drivercurrent source to provide a first uniform magnetic field H along theaxis of the coils which coincides with the easy axis of magnetization ofthe magnetic material in the channels 21 and 31 and a second set ofHelmholtz coils connected to a second driver current source to provide asecond uniform magnetic field H along the axis of these coils of thesecond set which coincides with the hard axis of magnetization of themagnetic material in channels 21 and 31. The coils are arranged toproduce a substantially uniform magnetic field in the region occupied bythe registers 20 and 30. The direction of each of the magnetic fields Hand H can be reversed simply by reversing the direction of currentsupplied to the coils from the corresponding driver current sources. Forthe magnitude of magnetic fields applied during operation of the storagedevice, only the portion of the film within the relatively low coerciveforce channel is capable of being switched. An output sensing coil 37positioned adjacent the end of data channel 31, while marker sensors 27and 28 coupled to the marker channel 21 at opposite ends thereof assistin determinin-g that the data register 30 is full or empty,respectively. In order to permit undesirable transfer or coupling ofmagnetic domains from the data channel 31 of data register 30 to themarker channel 21 of marker register 20, two techniques are shown anddescribed. One such technique involves flattening the upper apices ofthe data channel 31, as shown in FIGS. 1, 2, 6, 8 and 10; with thisconfiguration, one effectively obtains a m gnetic diode which permitsdomain transfer only along the direction from the marker channelsegments with pointed apices to the data channel segments with bluntedapices. Another technique for providing one-way domain growth isillustrated in FIGS. 12 and 13 and involves the use of an additionalcontrol wire traversing the data channel 31 about midway between theupper and lower apices thereof. When this latter technique is employedand the current is supplied to the additional control wire 90, the needfor blunted apices in the data channel 31 is obviated.

In order to understand better the operation of the shift registeraccording to the invention, a brief description of the basic shiftoperation cycle will be described with reference to FIGS. 2 to 4. Indescribing the basic shift cycle, only the upper (marker) register 20 ofFIG. 2 will be mentioned. The remainder of the shift register in FIG. 2will be referred to later during discussion of the write operation. Thebasic shift cycle consists of two sets of growing and shrinking steps.In FIG. 2a, a magnetic domain 40 is disposed at the apex or region ofintersection of adjoining segments 43 and 44 of marker channel 21. Thedirection of magnetization of this domain 40 is illustrated as upward;the background magnetization will be in the opposite direction, ordownward. A current I flowing in control wire 25 in the directionindicated will produce a magnetic field wherein lines of force betweenthe wire 25 and the channel 21 are in the same direction as lines offorce of the domain 40. In FIG. 2, as in all subsequent figures, thewires will be assumed to be over the channels. The magnetic fieldproduced by the current I is such as to enhance the magnetization of themagnetic domain and tends to maintain the domain in the vicinity ofcontrol wire 25, thereby preventing total disappearance of said domainduring the previous shrinking operation.

In FIG. 2b, the registers 20 and 30 are subjected to two perpendicularmagnetic fields H and H the first being directed either up or down (theeasy axis magnetization of the channel material) and the second beingdirected either to the left or right (the hard axis of magnetization).The means for producing such fields are well known in the art and, inlieu of the Helmholtz coils, already mentioned, the field producingmeans can comprise two flat spiral coils positioned adjacent the tworegisters and in a plane parallel to said registers, with the turns ofsaid coils being oriented such that the fields produced by the two coilsare mutually perpendicular.

If one desires to grow the domain of FIG. 2a, the easy axis ofmagnetization is such as to enhance the original magnetization of thedomain. In other Words, the easy axis magnetic field H in FIG. 2bproduced by current in the Helmholtz coils is directed upwardly. Thehard axis magnetization produced by current in such coils will determinethe direction of growth of the magnetic domain. In FIG. 2b, where themagnetic domain is to be grown along the segment 44 (that is, to theleft), the hard axis field H will be directed to the right, so that theresultant magnetic field H formed by the two component fields H and H issubstantially in the same direction as the segment 44 of the channel 21along which magnetic domain growth is desired. The domain 40a shown inFIG. 2b has grown to occupy substantially the entire area of segment 44.

In FIG. 20, the magnetic domain 40a of FIG. 2b is shrunk to 40b byreversing the direction of the easy axis field so that now the easy axisfield H opposes the magnetization of the domain. During the shrinkingstep, the hard axis of H may be removed; if a hard axis field is used,however, the direction of the hard axis field will be a factor indetermining the path of shrinking. In FIG. 20, the hard axis field H isdirected to the left so that the combined magnetic field H is in thedirection of segment 44. The direction of shrinking along the path ofsegment 44 is dependent upon the control currents applied to the controlwire 26. For example, when holding current I in control wire 26 flows inthe direction shown in FIG. 20, a magnetic field is created which aidsthat of the domain to be shrunk in the vicinity of the region ofintersection of segments 44 and 45 and the domain 40b has shrunk to theregion of intersection of the segments 44 and 45 adjacent control wire26. The magnetic field produced by applying current '1 on control wire26 either before or during the shrinking period also prevents the domainfrom shrinking entirely.

In FIG. 2d, the magnetic domain is grown to the left along segment 45 ofthe channel 21, as indicated at 400. The easy axis field H must bedirected so as to enhance the magnetization of the domain to cause thisgrowth; furthermore, the hard axis field H is directed to the left sothat the resultant magnetic field H is along the direction of segment45. The current I in wire 26 either can be left on or removed duringgrowth of the magnetic domain 40c along segment 45 in FIG. 2d.

Finally, (see FIG. 2e) the magnetic domain is shrunk,

as shown by reference numeral 40d, to the region of intersection ofsegments 45 and 46 by application of a shrinking magnetic field H,,, andby a hard axis field H if used, so oriented that the resultant magneticfield vector H is along the path of shrinkage, that is, along thesegment 45. A holding field is applied by means of the current I tocontrol wire 25 to prevent total shrinkage of the magnetic domain 40d.During one shifting cycle shown in FIGS. 2a to 2e, therefore, themagnetic domain 40 has been shifted from one of the upper regions ofintersection of channel segments to the upper region of intersection ofchannel segments immediately to the left.

The basic shift cycle for shifting. to the left, in cases in which themagnetic vector of the magnetic domain is directed downwardly, is shownin FIGS. 3a to Be and need not be described in detail. Since the basicshift cycle can be explained without reference to the data register,only the marker register is shown in FIGS. 3 and 4. The two magneticbiasing fields H and H, in FIGS. 3b to 32 are oppositely directed fromthose shown in FIGS. 2b and 2c, respectively. Likewise, the holdingcurrents I and 1,, in FIG. 3 are in opposite directions from those ofFIG. 2 since the magnetic field produced thereby should aid thedownwardly directed field within the magnetic domain during the growthsteps.

It is possible to shift the magnetic domain to the right, rather than tothe left, by reversing the hard axis mag netization during the growingand shrinking steps. Such operation is shown in FIGS. 4a to 40. In theoperation in FIG. 4, the magnetic domain is assumed to be magnetizedwith the vector directed upwardly, as in the case of FIG. 4. Again, itshould be noted that a reversal of direction of magnetization of themagnetic domain must be accompanied by a reversal in the direction ofthe applied biasing magnetic field.

Returnng now to FIG. 2, an explanation of the process of writing a databit into the data register 30 will be described. In FIG. 2a, a markerdomain 40 is disposed at the apex formed by the intersection of segments43 and 44 of the marker register. Holding currents 1,, and I remainflowing through control wires and 26 of respective marker and dataregisters 20 and 30 from some previous operating cycle. These currents Iand I are used during shrinking of the magnetic domain to prevent totalshrinkage. The first step in the write operation is to grow the magneticmarker domain 40 of FIG. 2a to a position 40a as shown in FIG. 2b. Theholding current I is removed from control wire 25. As already describedin connection with the basic shift operation, a pair of perpendicularmagnetic fields H and H, are presented to the shift registers, as shownin FIG. 2b. Owing to the proximity of the lower apices of register 20and the upper apices of register 30, there is a tendency for themagnetic domain to transfer across the gap between registers 20 and 30during this growing step. In order to prevent this transfer or couplingbetween registers 20 and 30, an inhibiting current I is supplied tocontrol wire of data register 30 in the direction indicated in FIG. 2b.The field lines produced by this current I are such that the magneticfield produced by this inhibiting current opposes the magnetization ofthe magnetic marker domain a. At the conclusion of the growing step, theentire region of segment 44 of marker register 20 is occupied by thegrown magnetic domain 40a. The next step in writing information into thedata register is to shrink the marker domain along segment 44 to 40b, asshown in FIG. 20. In order to favor shrinkage in a downward direction toa lower apex of marker register 20, as shown in FIG. 20, a holdingcurrent I is passed through control wire 26 of the marker register 20 inthe direction shown in FIG. 20 so that the lines of force set up by thiscurrent enhance the magnetization of the magnetic domain in the regionof intersection of segments 44 and 45. This holding current thus favorsshrinkage in the downward direction and precludes the possibility of themagnetic domain shrinking toward the upper apex of segment 44. It shouldhe noted that the path of shrinkage of the magnetic domain issubstantially along the direction of the resultant vector shown in FIG.2c and could be either up or down along the path. During the nextwriting step shown in FIG. 2d, the domain 40b in FIG. 20 is grown to 400which occupies substantially the entire area of segment 45 of markerregister 20. This is accomplished by means of the magnetic fields H andH in FIG. 2d, together with the inhibiting current I flowing in controlwire 35 of data register 30. This inhibiting current prevents thetendency of the magnetic domain to grow into segment 52 of data register30. The control current I can be removed from control wire 26 during thegrowing step of FIG. 2d, since it is not needed; this current does noharm, however, if left in wire 26. The final step in writing involvesshrinking the domain shown in FIG. 2e to the upper apex at theintersection of segments 45 and 46 of marker register 20 (see domain40d) by applying the two magnetic biasing fields H and H shown in FIG.2e and by passing a holding current I in control wire 25 of markerregister 20. This holding current 1,, tends to favor shrinkage in thedirection of the upper apex 49 underlying the wire through which theholding current passes. Although not necessary in writing a ZERO intodata register 30, a holding current I is pased through control wire 36of data register 30 during the final writing step shown in FIG. 2e,since there may be ONEs in the data register which must be kept fromshrinking entirely off the data register during the final shrink step.At the conclusion of the writing operation, the marker domain 40 appearsat upper apex 49 of marker channel 21. In other words, marker domain 40has been shifted one position to the left while a ZERO, that is, theabsence of a magnetic domain in data register 30, appears at the lowerapex 59 of channel 31 of data register 30. This ZERO data bit occupies aposition along the data register 30 corresponding to the position along,the marker register 20 occupied by the marker bit 40d.

The manner in which a ONE is written into the data register will now bedescribed with reference to FIGS. 2a, and 2 to 211, inclusive. Prior tobeginning of the operating cycle for writing a ONE into the dataregister 30, the marker domain 40 is shown in FIG. 2a as occupying aregion formed by the intersection of segments 43 and 44 of markerregister 20. As previously explained, prior holding currents I, and Ipass through control wires 25 and 36, respectively. The first step inthe operating cycle involves growing the marker domain along segment 44or marker channel 21, as shown in FIG. 2f. This is accomplished byapplication of two mutually perpendicular magnetic biasing fields H andH, shown in FIG. 2 to the two registers. The holding currents I and 1,,are removed, if they have not already been removed. As was notedpreviously, there is a normal tendency, owing to the proximity of theadjacent apices of the two registers,

7 for the magnetic domain in the marker register to transfer or coupleacross into the segment 53 of the data register during the growingperiod. It will be recalled that, in the case of a ZERO to be writteninto the data register, this tendency was inhibited by means of aninhibiting current I passed through the control wire 35 of data register30. When a ONE is to be written into the data register, however, thisinhibiting current I in control wire 35 is removed; in this manner, thenormal tendency of the magnetic domain 40a to grow across into thesegment 53 of the data register 30 is encouraged and a magnetic domain60a occupies substantially the entire area of the segment 53 of dataregister 30. It is during the first growing step, shown in FIGS. 2b and2 that the writing for a ZERO and a ONE basically differ. During theshrinking step shown in FIG. 2g, the direction of the easy axismagnetization H is reversed and holding currents I and I are passedthrough the wires 26 and 36 of respective registers and 30, therebyfavoring. shrinkage of the domains previously in FIG. 2g to the lowerapices. As a result of the shrinking operation, domain 40b appears atthe lower apex of marker channel 21 shown in FIG. 2g and now a shrunkendomain 60!) appears at the lower apex 59 of data channel 31. During theshrink interval of FIG. 2g, the inhibiting current I can be supplied tocontrol wire 35, although its absence during this step is not critical.Next follows a second growing step wherein magnetic fields HI and H, areapplied as shown in FIG. 211 to establish a tendency for growth of themarker and data domains along respective segments 45 and 54 of the tworegisters. The inhibiting current I passed through wire 35 of dataregister 30 during this time accomplishes two purposes. First, itprevents transfer of domain 400 along the resultant magnetic vector ofthe two biasing fields into the segment 52 of data register 30. Second,this current inhibits full growth of the domain 600 along segment 54 ofdata register 30 and up into the segment 47 of marker register 20.Finally, as shown in FIG. 2i, a shrinking field is applied to the tworegisters. The path along which shrinkage will be accomplished isindicated approximately by the direction of the resultant vector H ofthe two magnetic fields. Holding currents I and I are applied to controlwires and 35- of marker register 20 and data register 30, respectively.These holding currents favor shrinkage to the upper apex 49 of themarker channel 21 and to the lower apex 59 of the data channel 31. Atthe conclusion of the writing cycle shown in FIGS. 27 to 21', a ONE(data domain 60d) is written into the lower apex 59 at a position alongthe data channel 31 corresponding to the position of the marker bit(magnetic domain 40d) in the marker register 20. In normal operation,the inhibiting current I in wire 35 of the data register will be left onat all times during the writing operation except during the one stepshown in FIG. 2 in which transfer of the magnetic domain during growthfrom the marker register to the data register is to be accomplished. Insome instances, as for example, in the steps shown in FIGS. 2g and 21',this inhibiting current need not be applied. However, for drive circuitsimplicity, this currentusually is maintained in control wire of dataregister- 30 except in the instance above cited when a ONE is to bewritten into the data register.

In order to facilitate understanding of the writing operation, waveformsare shown in FIG. 5 indicating the currents supplied to the two magneticfield biasing producing means and the four domain controlling wires ofthe two shift registers. The time intervals indicated in FIG. 4 as 1, 2,3 and 4 correspond, respectively, to the intervals illustrated in FIGS.1b, 1c, 1d, and 1e, respectively, or FIGS. 1f, 1g, 1h, and 11',respectively. In those portions of the operating cycle in which thecurrents are optional, this choice is indicated by dotted lines. In FIG.5e, the waveforms during interval 1 differ for a ONE and a ZERO. Thisdifference is indicated by the reference numerals 1 and 0.

The manner in which information is read out of the data register isshown in FIG. 6. In FIG. 6a the marker bit is shown at an upper apex 49of the marker channel 21 and the data bit 60 in this case a ONE, isshown at a lower apex 59 of data channel 31. Holding currents I and Iare supplied to the domain-controlling wires 25 and 36 of the tworegisters from a previous cycle. In FIG. 6b, the growth of the twodomains is illustrated. A pair of mutually perpendicular magnetic fieldsare produced, as shown in FIG. 611, so that the resultant magneticvector I-I is approximately in the direction of the segments and 54 ofthe two registers along which the magnetic domain growth is to beaccomplished. An inhibiting current I is applied to control wire 35 ofdata register 30 to prevent growth of the domain 40a into the segment 52of data channel 31. This inhibiting current I further prevents totalgrowth of the magnetic domain a in the segment 54 of the data channel 31up to the apex '58 and into segment 47 of marker register 20. In FIG.6c, a shrinkage operation is shown wherein the magnetic fields arereversed from those shown in FIG. 6b and the holding currents I and Iare passed through the respective domain controlling wires 26 and 36 ofthe registers 20 and 30. At the conclusion of this shrinking cycle, theshrunken domains 40]) and 60b exist at lower apices of the two registersshown in FIG. 60. In the next step, illustrated in FIG. 6a, the domains40b and 60b of FIG. 60 are grown to the right by applying the magneticfields shown in FIG. 6d, and by permitting an inhibiting current I toflow in the domain controlling wire 35 of the data register 30. With thecurrents and fields shown in FIG. 6d, the domain 400 in segment 44 ofthe marker register occupies substantially the entire area thereof andthe domain 60c in segment 53 of the data register is grown partiallyalong the segment 53. Next, as shown in FIG. 62, the domains are shrunkby application of a shrinking fields and by the application of holdingcurrents I and I At the conclusion of this shrinking period, shown inFIG. 62, the marker bit 40d now resides at the upper apex 63 forming theintersection of segments 43 and 44 of marker channel 21 and the data bit60d is located at the lower apex 59 formed by the intersection ofsegments 53 and 54 of the data channel 31.

It will be noted that in the operating steps shown in FIGS. 6a to 6e,the data has remained centered about the apex 59 of the data channel 31whereas the marker bit 40 has been moved to a position one upper apex tothe right of that in which it formerly existed. In the remaining stepsof this read cycle, illustrated in FIGS. 6 to 6i, the marker will beheld centered about the upper apex 63 of marker register 20 while thedata is moved to the right. With the magnetic biasing fields as shown inFIG. 6 and with the current I in wire 26 of marker register 20 in thedirection shown in FIG. 6 the domains of FIG. 6e are grown as indicatedin FIG. 6 along segments 44 and 53 of the respective channels 21 and 31.Because of the inhibiting effect of the current 1 the domain (We growingin segment '53 of data channel 31 will not be transferred into thesegment 44 of the marker channel and the domain 40e growing alongsegment 44 of marker channel 21 will remain within the con-fines ofsegment 44 of the marker register, rather than being transferred acrossto the segment 53 of data channel 31. In FIG. 6g, the magnetic fieldshave been reversed and holding currents I and I supplied to wires 25 and35 of the two registers 20 and 30, respectively. The inhibiting currentI in wire 26- can now be removed. The two domains shrink to upper apicesof the respective registers as shown at 40] and 60 In FIG. 6h a growingtfield is supplied to the registers, and inhibiting current I againsupplied to the control wire 26 of marker register 20. The holdingcurrents I and I can now be removed. The current 1,, in control wire 26prevents the marker domain 40 from growing to the lower apex of themarker channel 21. During the operating step shown in FIG. 611, the databit or data magnetic domain 60g will grow alongthe final segment 52 ofthe data register 30 and will pass the sensing coil 37 surrounding thisfinal segment. As this magnetic domain grows past the sensing coil 37,an output voltage will be induced in the sensing coil; in other words, aONE output will be derived. In the final step of the read cycle, shownin FIG. 6i, holding currents I and I are supplied to wires 25 and 36 ofthe respective marker and data registers and 30. During this final step(FIG. 6i), the shrinking field is applied to the registers such that themarker domain 40h is shrunk to the upper apex 63 of the marker channel21 in the vicinity of the wire 25 through which the holding current I isflowing. The holding current I is needed to facilitate shrinkage of datadomains in the data register toward the lower apices of the dataregister and to maintain the data magnetic domains at these lower apicespending the start of another read cycle. It will be evident that duringthe portion of the read cycle shown in FIGS. 6 to 6i, the marker bit 40has been substantially fixed in position, while the data domain 60 hasbeen moved one position to the right. When the marker has reached theextreme point along the register, external means, not forming a portionof this invention, indicates this attainment of the extreme position andno further reading will be achieved until such time as the marker hasbeen appropriately moved to another position along the marker register.

Typical waveforms showing the currents applied to both the hard and easyaxis magnetic field producing means and to the domain controlling wiresof the two registers are shown in FIG. 7. As previously explained, onecan dispense with hard axis field during the shrinking period; this isindicated in FIG. 7 by the dotted portion of the waveforms. The periodsindicated in FIG. 7 as 1 to '8 inclusive correspond to the steps of theread cycle shown respectively in FIGS. 6b to 6i. As in the case of thewaveforms shown in FIG. 5, the current supplied to the easy and hardaxis field producing coils is bipolar. During the reading cycle, asshown in FIGS. 7d and 7c, the drives for the domain controlling wires 26and are also bipolar.

A modification of the shift register of FIGS. 1, 2, 4 and 6 is shown inFIGS. 8 and 10. In the shift register shown in FIG. 8, a fifth domaincontrolling wire 70 is positioned between the two registers, in additionto the four domain controlling wires 25, 26, 35 and 36. When this fifthwire is used, one does not need to shift the marker and the dataregisters separately during the reading operation. The basic writingoperation with this fifth wire system is shown in FIG. 8. With the fifthwire system, it will be noted that the data bits are stored in the upperportions of the data register, rather than at the lower portionsthereof, as in the case of the previously designed shift register. InFIG. 8a, a ONE (data domain 80) has been stored at an upper apex formedby intersection of segments 53 and 54 of the data channel 21 and themarker domain is positioned at an upper apex formed by the intersectionof segments and 46 of the marker channel 21.

Assume now that a ONE (data domain 80) already has been written into thedata register 30. In FIG. 8b, the domains of FIG. 8a are grown, by meansof a growing field indicated in FIG. 8b, along the direction of theresultant vector H of the two magnetic fields applied to the registers.No current is passed through the fifth control wire 70 at this time; inother words, I =0. The marker domain 40 of FIG. 8a grows through theentire region of the segment 46 of the marker channel into a do main 40aand is transferred into the data register 30 to form data domain a whichessentially fills the segment 56 of the data channel, At the same time,the data bit 80 FIG. 8b. In FIG. 80, a shrinking step is shown andmagnetic fields H and E are applied in the direction indicated. Inaddition, current I passes through the control wire and holding currentsI and I are supplied to the control wires 26 and 35, respectively. Theholding current I prevents the domain 40b from shrinking upwardly alongsegment 46 and current I prevents the domains 60b and 80b from shiftingdownwardly along respective segments 56 and 54 of the data register. Thecurrent I in the control wire 70 inhibits transfer of the domains fromone register to the other. In the step illustrated in FIG. 8d, a growingfield is applied to the two registers and the holding currents I and Iare removed. The control current in control wire 70- is still applied tothis control wire to prevent growth from one register to the other. Thedomain 40c in the marker register (see FIG. 8d) grows along segment 47thereof and the domains 60c and 80c in the data register 30 extend alongthe segments 53 and 55 to occupy substantially the entire area thereof.In FIG. 8e, the shrinking operation is shown wherein the domains are allshrunk to the upper apices indicated. The holding currents I and I againserve to facilitate shrinkage in the proper direction. At the conclusionof this shrinking operation shown in FIG. 8e, it will be noted that anadditional ONE (data domain 6011) has been written into the data channel31 at apex just behind the ONE (domain d) previously written therein atapex 74.

FIGS. 8a and 8 to 81 illustrate the manner in which a ZERO is writeninto the data regster. The marker domain and the ONE bit originally areas shown in FIG. 8a. Durign the first step in the writing operation, asshown in FIG. 8 the basic distinction between Writing a ZERO and writinga ONE is shown. In writing a ONE, it will be remembered from FIG. 8bthat the control current I was reduced to ZERO during the growing cycleand the marker domain was allowed to transfer into the data register. Inthe case of a ZERO, however, as shown in FIG. 8], the growth of a markerdomain into the data register must be inhibited. This is done by meansof the control current I allowed to flow in control wire 70 during thisperiod. With the application of the necessary growth fields, the domainsof FIG. 8a are grown along the segments 46 and 54, as indicated in FIG.8f. The resulting domains are indicated as 40a and 80a. In FIG. 8g, ashrinking step is shown with the magnetic fields being reversed fromthose shown inFIG. 8 and the holding currents I and I now flowing in thecontrol wires 26 and 35 of the marker and data registers. The controlcurrent I continues to flow in control wire 70. At the conclusion of theshrinking cycle shown in FIG. 8g, the marker domain 40b has shrunk tothe lower apex of channel 21, and the ONE data bit already in dataregister 30 has shrunk as shown at 8012 to the upper apex of channel 31.The next step is shown in FIG. 8h wherein a growing magnetic field isapplied to the registers and the holding currents I and I can be removedfrom respective control wires 26 and 35. The marker domain grows alongsegment 47, as indicated at 40c and the ONE data bit grows along thesegment 53, as indicated at 80c. Interregister transfer is inhibited bythe control current I in control wire 70. The final step in writing aZERO into the data register is shown in FIG. 8i wherein a shrinkingfield is applied to the registers. The control current I in control wire70 is still flowing, as in the case of FIGS. 8 to 8h. The controlcurrent, in this case, assists in determining the direction of shrinkageof the domains along segments 47 and 53 and permits the domain 40d insegment 47 of FIG. 81 to shrink to the upper apex 66 of the markerchannel 21 and permits the data domain 80d to shrink to the upper apex74 shown in FIG. 8i of data channel 31. At the conclusion of the writingcycle, it will be noted that there is no magnetic domain at the apex 75next to the data domain in apex 74. In other words, a ZERO has beenwritten into the data register at the apex 75.

The waveforms of the currents supplied to the coils of the magneticfield producing means and to the various domain controlling wires isshown in FIG. 9. The intervals designated in FIG. 9 as 1, 2, 3 and 4 arethe intervals shown, respectively in FIGS. 8b, 8c ,8d and 8e or inFIG-S. 8g, 8h, 81 and 8j. The reading operation for this five-wiresystem is shown in FIG. 11.

At the beginning of the read cycle, as shown in FIG. 10a, the domainsare just as they were in FIG. 82, that is, the marker bit 40 is at theupper apex 66 in marker register and two successive ONE data bits 80 and60 are located at adjoining upper apices 74 and 75 of the data register30. Upon application of a growing field to the registers, as shown inFIG. 10b, and, with a control current I applied to control wire 70, themarker domain 40w grows down along the segments 53 and 55 of the datachannel 31. Interregister transfer of domains is prevented by thecontrol current I in line 70. In FIG. 10c, a shrinking step is shownwherein the shrinking fields are applied to the two registers, togetherwith the holding currents I and I on control wires 26 and 36,respectively. Although, in the shrinking step we do not need the controlcurrent I it is normally left flowing at all times during the readingprocess. The marker domain 40b shrinks around the lower apex in thevicinity of the holding current I in control wire 26 and the datadomains 80b and 60b shrink down to the lower apices in the vicinity ofthe holding current I in control wire 36. The next step is shown in FIG.10d wherein growing fields are applied to the registers and the holdingfields can be removed from about wires 26 and 36. The control current Iin wire 70- prevents inter-register transfer of domains 80c and 60c. Asthe right-hand data domain 80c grows along segment 52 of the dataregister 30, it passes the sensing coil 37 and causes a voltage to beinduced in said coil. In other words, a ONE is read out of the dataregister. Finally, as shown in FIG. 10c, a shrinking field is applied tothe registers, together wth the holding currents I and I in controlwires and 35, respectively, The marker domain 40a. then shrinks up tothe upper apex 73 in the vicinity of the control wire 25 and theremaining data domain 60d shrinks up to the upper apex 74 adjacent thecontrol wire 35. Again, the control current I in control wire 70 is notnecessary; however, it is easier to construct a control circuit, which,during the entire read cycle, has a constant output. This output isshown, incidentally, in FIG. 11 FIG. 11 shows a waveform of the currentsupplied to the magnetic field producing means and to the various driverwires. It will be noted that, with the five-wire system, during thereading operation, all inputs to the driver wires are monopolar, incontrast with the waveforms in the reading operation of the four-wiresystem. For example, referring back to FIG. 7, it is noted that thedriver currents I and I during the read operation for the fourwiresystem will require bipolar devices. No such devices would be requiredfor driving currents with a five-wire system, however. Bipolar devicesare more difficult to im plement than monopolar devices and some of thedrive circuits for the five-wire system thus are somewhat simplified.

In FIG. 12, a modification of the four-wire system of FIG. 2 is shown inwhich an additional control wire 90 is positioned substantially alongthe longitudinal axis of data register 30 to prevent bilateral transferof magnetic domains between marker and data registers 20 and 30. Thisapproach does away with the need for blunting the upper apices of datachannel 31, described in FIGS, 1, 2, 6, 8 and 10.

With the modification shown in FIG. 12, the first growing periodrequires two separate steps with different control currents (see FIGS.12b and 120) as compared with the single-step growing operation shown inFIG. 2f. In FIG. 120, it is assumed that initially a ONE data bit 80already has been written into a lower apex of data register 30 shown inFIG. 12a and that the marker bit is at a juxtaposed upper apex of markerregister 20. The currents I,,, I and I are applied, just as in thedevice of FIG. 20.

If a ONE is to be written into data register 30', growing magneticfields H and H are applied, as indicated in FIG. 12b, and controlcurrent I in control wire 35 is removed. In FIG. 12!), as contrastedwith FIG. 2), however, an added driver current I is supplied to thedevice. The driver current I is applied to the additional control wire90 of the data register 30 in a direction such as to oppose growth ofthe magntic domain 60a, transferred from marker register 20, to thelower end of segment 55 of channel 31 and prevents growth of data domaina to the upper end of segment 53 of the data channel 31. In this manner,undesirable transfer of the data domain 80a from segment 53 of datachannel 31 into segment 44 of marker channel 21 is precluded. During thesecond portion of the first growth operation shown in FIG. 120, thecontrol current I in control wire is removed and the control current Iis supplied to control wire 35. It should be noted that during theoperation shown in FIG. 120, the control current I must be applied tocontrol wire 35 at least slightly prior to removal of control current Ifrom control wire 90. This can be done by properly timing the generationof control pulses I and I The domains 40b, 60b and 80b of FIG. 12cremain substantially as shown in FIG. 12b, except for slight extensionof the data domains 60b and 80b; full growth of these data domains 60band 80b is prevented owing to the presence of current I in control wire35. The marker domain 40c and data domains 60c and 800 of FIG. 12d areshrunk by application of the magnetic shrinking fields and byapplication of holding current I and L, to control wires 26 and 36,respectively. The control current I remains flowing in control wire 35.The marker domain 40d is grown, as shown in FIG. l2e, along segment 47of marker channel 21 and the data domains 60d and 80d are grown alongrespective segments 56 and 54 of data register 30 by means of thegrowing magnetic fields. Full growth of the data domains 60d and 80d tothe upper apices of respective segments 56 and 54 is prevented by thecurrent I in control Wire 35. Finally, as shown in FIG. 12f, the markerdomain 40:: is shrunk to the upper apex terminating segment 47 of themarker channel 21 and the data domains 60e and 8% are shrunk toadjoining apices of data channel 31. During this shrinking period theholding currents 1, and I are supplied to respective control wires 25and 36, in addition to the control current I in control wire 35. Itshould be noted that a ZERO could have been Written into the dataregister 30 by applying a control current I to control wire 35 of dataregister 30 in the operation shown in both FIGS. 12b and 12c. In otherwords, to write a ZERO into data register 30, a control current I inFIG. 12b would be applied to control wire 35; furthermore, the current Iin control wire 90 in FIG. 12b would be optional. In the case of a ZERO,therefore, the two portions of the first growing operation shown inFIGS. 12b and 12c could be identical; it is only when a ONE is to bewritten into the data register that the two portions of the firstgrowing operation must be ditferent, as shown in FIGS. 12b and 120. Inpractice, however, ONEs and ZEROs appear in indeterminate sequence, sothat both portions of the first growing operations shown in FIG. 12b and12c are necessary.

In FIG. 13, modification of the five-wire system of FIG. 8 is shownwhere an additional control wire 90, similar to that shown in FIG. 12crosses the channel 31 of the data register 30 about midway between thelower and upper apices. The purpose of the added control wire 90 of FIG.13 is the same as that of control wire 90 of FIG. 12.

As shown in FIG. 13a, a marker bit 40 is shown in an upper apex ofmarker register 20 and the data bit is assumed to have been written intoan upper apex of data register 30. This is the same conditionillustrated in FIG.

8a. Assuming that one desires to write a ONE into the data register 30,the first growing operation is shown in FIGS. 13b and 13c, whichcontrasts with the single-step growing operation shown in FIG. 8b. InFIG. 1312, the control currents I and I are removed from control wires25 and 36 and the current I from control wire 70. A control current I issupplied to control wire 90; this current I,, inhibits growth of thedomains 60a and 80a to the lower and upper apices terminatingrespectivesegments 56 and 54 of data register 30. This portion of theoperation shown in FIG. 13b prevents reverse transfer of data domain8'0a into the segment 44 of the marker register 20. During the secondportion of the first growing operation, shown in FIG. 130, the controlcurrent I is removed from control wire 90 and the control current I issupplied to control wire 70. The data domains 60b and 80b then continueto grow to the adjoining upper apices of data channel 31 shown in FIG.13b. Note that, in FIG. 130, the control current I in control Wire 35must be applied at least slightly before removal of control current Ifrom control wire 90. In FIG. 13d, a shrinking magnetic field is appliedand control currents I and I supplied to respective control wires 26 and35, in addition to the currents supplied in FIG. 13c. The marker domain40c shrinks to a lower apex of marker channel 21 terminating segment 46of channel 21 and the data domains 60c and 80c are shrunk to theadjoining upper apices of data channel 31 terminating respectivesegments 56 and 54 of data register 30.

In the seconcl growing step, shown in FIG. 1-3e, the marker domain 40dis grown along segment 47 of marker channel 21 and the data domains 60dand 80d "are grown along respective segments 55 and 53 of data channel31. In FIG. 13e, the holding currents I and I of FIG. 13b are removedfrom control wires 26 and 35. Finally, as shown in FIG. 13f, the markerdomain 40:: isshrunk to the upper apex 66 past which holding current I,,flows and data domains 60a and 80e are shrunk to the upper apices 75 and74 past which the holding current I flows.

As stated in connection with the device shown in FIG. 12, if only ZEROswere to be written into the data register 30 the two separate portionsof the growing operation, shown in FIGS. 13b and 130 could be identical,since the control current I should flow through control wire 70 duringboth portions of this first growing operation. The current I in controlwire 90 then would be optional. How ever, in practice since ONEs andZEROs occur in mixed sequence, the two portions of the first growingcycle are maintained for both ONEs and ZEROs.

What is claimed is:

1. A first-in, first-out memory including a marker shift register, adata shift register contiguous with said marker shift register, both ofsaid shift registers having a plurality of discrete storage locations,said marker shift register containing a magnetic marker domain disposedtherein at a controllable discrete storage location, means for movingsaid magnetic marker domain along said marker shift register inincrements of one storage location, and means for writing data in theform of a magnetic domain into said data shift register at one discretelocation thereof determined by the location in said marker shiftregister of said marker domain.

2. A first-in, first-out memory according to claim 1 further includingmeans for reading data out of said data shift register from one discretelocation thereof disposed at one end of said data shift register.

3. A first-in, first-out memory according to claim 1 wherein each ofsaid shift registers are multi-segmented channels of magnetic materialmounted directly upon a common magnetic medium of higher coercivity.

4. A first-in, first-out memory according to claim 1 wherein each ofsaid shift registers includes a single sawtooth-shaped channel ofmagnetic material consisting of a plurality of individual segmentsintersecting to form a series of adjoining upper and lower apices, agiven segment of said marker shift register channel being aligned withand adjacent to a corresponding segment of said data shift registerchannel.

5. A first-in, first-out memory according to claim 2, wherein each ofsaid registers includes a single multisegmented channel of magneticmaterial of relatively low coercivity; said writing and reading meansincluding current driver means, magnetic domain-controlling electricallyconductive means and means for producing magnetic fields directed alongthe hard axis and easy axis of magnetization of said channel; saidconductive means and said means for producing being selectively drivenby said current driver means.

6. A first-in, first-out memory according to claim 2 wherein each ofsaid registers includes a single multi-segmented channel of magneticmaterial of relatively low coercivity; said writing and reading meansincluding current driver means, magnetic domain-controlling electricallyconductive means and means for producing magnetic fields directed alongthe hard axis and easy axis of magnetization of said channel; saidconductive means and said means for producing being selectively drivenby said current driver means.

7. A first-in, first-out memory according to claim 5 wherein said meansfor writing includes means for growing said marker domain into said dataregister under control of said driver means to write a binary ONE intosaid data register. 1

8. A first-in, first-out memory according to claim 5 wherein said meansfor writing includes means for inhibiting growth of said marker domaininto said data register under control. of said driver means to write abinary ZERO into said data register.

9. A first-in, first-out memory according to claim 5 wherein each ofsaid shift registers is traversed by a pair of said conductive means.

10. A first-in, first-out memory according to claim 9 wherein transferof said marker domain into said data shift register is dependent uponthe mode of driving one of said conductive means.

11. A first-in, first-out memory according to claim 9 further includinga domain-controlling conductive means disposed between said data shiftregister and said marker shift register for controlling inter-registertransfer of said marker domain.

12. A first-in, first-out memory according to claim 5 further includinga domain-controlling electrically conductive member traversing said datashift register substantially along the longitudinal axis thereof forcontrolling inter-register transfer of said domains.

13. A first-in, first-out memory according to claim 12 further includinga domain-controlling electrically conductive member disposed betweensaid data shift register and said marker shift register for controllinginter-register transfer of said domains.

References Cited UNITED STATES PATENTS 3,438,006 4/1969 Spain 3401743,113,297 12/1963 Dietrich 340- 174 3,114,898 12/1963 Fuller 3401743,140,471 7/1964 Fuller 340174 3,148,360 9/1964 Hale 340-474 3,212,07010/1965 Fuller et al 340174 STANLEY M. URYNOWICZ, JR., Primary Examiner

